The rim of Foster is slightly eroded, and the narrow inner walls slope directly down to the relatively dark interior floor.
The rim has a small outward bulge along the southwest side.
There is a small craterlet on the floor next to the northern rim.
A tiny impact in the southeast part of the crater interior is surrounded by a small skirt of high albedo material, producing a bright patch.
By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Foster.